docs: def _add_instruction(self, instruction, value):
          """
          :param instruction: instruction name to be added
          :param value: instruction value
          """
          if (instruction == 'LABEL' or instruction == 'ENV') and len(value) == 2:
              new_line = instruction + ' ' + '='.join(map(quote, value)) + '\n'
          else:
              new_line = '{0} {1}\n'.format(instruction, value)
          if new_line:
              lines = self.lines
              if not lines[len(lines) - 1].endswith('\n'):
                  new_line = '\n' + new_line
              lines += new_line
              self.lines = lines